Organic photochromic materials

ABSTRACT

The invention relates to transparent, photochromic or nonphotochromic organic materials, which have a refractive index higher than 1.55 and which are free of optical distortions, consisting of a copolymer of: 
     (a) 50-90 wt. % of at least one monomer represented by the formula,                    
     in which R═H or CH 3 , and m and n are independently 1 or 2; 
     (b) 10-30 wt. % of at least one aromatic monovinyl monomer represented by formula,                    
     R 1 ═H or CH 3 ; and 
     (c) 1-20 wt. % of at least one (meth)acrylic monomer represented by formula, 
     
       
         CH 2 =C(R)—COOR′ 
       
     
     in which R═H or CH 3    
     R′ is a straight-chain or branched C 4  to C 16  alkyl radical, an alkylaryl radical, or a polyoxyethoxylated group with formula —(CH 2 —CH 2 O) n R″ in which n=1 to 10 and R″═CH 3  or C 2 H 5 . Optionally, the photochromic material may contain up to 10 wt. % of at least one photochromic coloring agent to impart desired photochromic properties. 
     The material which may also contain up to 15 wt. % of an aromatic divinyl monomer represented by the formula                    
     where R 1 ═H or CH 3 ., may be polymerized in the presence of up to 0.5 wt. % of at least one non-peroxide radical polymerization initiator. 
     The organic material is particularly useful for the production of ophthalmic lenses and glazings for such objects as vehicles and buildings

The present application is 371 of PCT/US96/18668, filed Nov. 21, 1996,which claims the benefit of U.S. Provisional patent application Ser. No.60/011,429, filed Feb. 8, 1996; U.S. Provisional patent application Ser.No. 60/023,330, filed Jul. 31, 1996; and of French Patent ApplicationNo. 95 14343, filed Dec. 5, 1995.

BACKGROUND OF THE INVENTION

The invention relates to new transparent, photochromic andnon-photochromic organic materials, which have a high refractive indexwith no optical distortion in the mass, to a process for theirpreparation, and to articles formed from these materials.

The production of a photochromic ophthalmic lens made of plasticmaterial is very difficult. Ideally, the polymer matrix of such a lensshould be thermally crosslinked, should be free of optical distortion inthe mass, and should be capable of receiving and of being crosslinked inthe presence of appropriate mixtures of photochromic coloring agents,such as spiroxazines and chromenes, in order to obtain a material with ahigh initial transmission before exposure and an extensive darkeningcapacity after exposure, all this with rapid darkening and lighteningkinetics. Moreover, the material should have a low thermal dependence, ahigh fatigue strength, and a high refractive index.

Several materials have been suggested for making such materials. Forexample, WO-A-92/05209 describes a copolymer, which is free of opticaldistortions, which is suitable for manufacturing glasses for eyeglasses,which is obtained by radical polymerization of a first monomer havingthe following formula:

in which a and b are whole numbers from 0 to 4, R₁ and R₂═H or CH₃, andR₃═—O—, —S—, —CO—, —SO₂—, —CH₂—, —CH═CH— or CH₃—C—CH₃, with a secondmonomer which can be styrene or a styrene derivative, and optionally, athird monomer which can be an aromatic vinyl compound or an aromaticmethacrylate, in the presence of an initiator of the peroxide type and achain transfer agent chosen from various brominated compounds. While thecopolymer of the above reference may provide a polymer matrix for aphotochromic article, such as a lens, attempts to incorporatephotochromic coloring agents in the copolymerizable composition failedbecause the coloring agents tend to be destroyed by the peroxideinitiator. And even if the peroxide initiator is replaced by a gentlerradical polymerization initiator, such as a diazoic compound such asazo-bis-isobutyronitrile, the material which is obtained is stillunsatisfactory because the photochromic coloring agents are inhibited bythe brominated chain transfer agent which is used, as the presentinventors were able to observe.

One method which has been suggested for overcoming the above problems isto incorporate the coloring agents in the matrix after polymerization,for example, by a thermal diffusion process. However, such a processtends to be inefficient, adds to the manufacturing cost of the materialand complicates its process of manufacturing.

In order to remedy the above problems, co-pending, co-assigned FrenchPatent Application No. 95 08424, filed Jul. 12, 1995, for “Newphotochromic organic materials,” (herein incorporated by reference),discloses a new transparent photochromic organic materials having arefractive index greater than 1.55 and free of optical distortions,obtained by radical polymerization of a polymerizable compositioncontaining:

a) 80 to 95 wt % of at least one monomer represented by general formula(I):

in which R═H or CH₃, and m and n are independently 1 or 2;

b) 5 to 20 wt % of at least one aromatic monovinyl monomer representedby general formula (II):

where R₁═H or CH₃

c) optionally, up to 10 wt % of an aromatic divinyl monomer representedby the general formula (III):

where R₁═H or CH₃.

d) an effective quantity of at least one coloring agent giving thematerial photochromic properties, chosen from the group of thespiroxazines, spiropyrans and chromenes;

e) an effective quantity of a chain transfer agent; and

f) an effective quantity of a radical polymerization initiator;characterized by the fact that the chain transfer agent is astraight-chain alkanethiol, and the radical polymerization initiator isa diazoic compound, as well as a process for preparation of thesephotochromic materials and photochromic articles consisting of thesematerials.

Although the photochromic materials described in the aforementionedFrench patent application represent a significant advance, therecontinues to be a need for organic materials which are easier andtherefore less costly to form into lenses free of optical defects

SUMMARY OF THE INVENTION

Briefly, the invention relates to new transparent organic photochromicand non-photochromic materials which have a refractive index higher than1.55 and which are free of optical distortions. In particular, theinvention relates to an organic material consisting essentially of acopolymer of:

a) 50 to 90 and preferably 55 to 70 wt % of units derived from at leastone monomer represented by general formula (I):

in which R═H or CH₃, and m and n are independently 1 or 2;

b) 10 to 30 and preferably 15 to 25 wt % of units derived from at leastone aromatic monovinyl monomer represented by general formula (II):

where R₁═H or CH₃;

c) up to 15 wt. %, preferably 2 to 6 wt. % of units derived from anaromatic divinyl monomer represented by general formula (III):

where R₁═H or CH₃;

d) 1 to 20 and preferably 5 to 15 wt % of units derived from at leastone (meth)acrylic monomer corresponding to the general formula (IV):

CH₂═C(R)—COOR′

in which R═H or CH₃,

R′ is a straight-chain or branched C₄ to C₁₆ alkyl radical, an alkylarylradical, or a polyoxyethoxylated group with formula —(CH₂—CH₂O)_(n)R″ inwhich n=1 to 10 and R″═CH₃ or C₂H₅, and

e) optionally, an effective quantity of at least one coloring agentgiving desired photochromic properties, chosen from the group of thespiroxazines, spiropyrans and chromenes.

In another aspect, the invention relates to an organic photochromic andnon-photochromic material which further includes at least onenon-photochromic coloring agent.

In still another aspect, the invention relates to a process for thepreparation of new transparent, organic materials, which have arefractive index greater than 1.55 and which are free of opticaldistortions, the process consisting of the radical polymerization of apolymerizable composition comprising: (a) the monomers of formulae I,II, III and IV as defined above; (b) optionally, an effective quantityof at least one coloring agent giving the desired photochromicproperties, chosen from the group of the spiroxazines, spiropyrans andchromenes; (c) optionally, an effective quantity of at least one chaintransfer agent chosen from a group consisting of the straight-chainalkanethiols, the alkanethiols substituted by at least one aryl or aradical, and the thiophenols; (d) an effective quantity of at least oneradical polymerization initiator, and (e) optionally, a hindered aminelight stabilizer.

In a further aspect, the invention relates to a method of making aatransparent organic material having a base tint by first forming atransparent organic material by the radical polymerization of components(a) through (e) as above, and subsequently applying a non-photochromicdye to the photochromic material. In yet another aspect, thenon-photochromic dye is combined with the polymerizable matrix so thatthe resulting photochromic material combines both photochromic andnon-photochromic dyes.

For the purposes of the present invention, the term “(meth)acrylic”means acrylic or methacrylic; and for ease of discussion, “organicmaterial” means either photochromic or non-photochromic transparentorganic materials.

DETAILED DESCRIPTION OF THE INVENTION

The organic material of the invention is characterized by having arefractive index greater than 1.55, and which is prepared by the radicalpolymerization of a plastic matrix. In the preferred embodiment, thecoloring agent is incorporated in the polymerizable composition toobtain directly, after polymerization, and optionally, an organicmaterial having desired properties. As a variant, it is also possible toproduce the organic material by first preparing a nonphotochromicmaterial by polymerization as described herein, and subsequentlyimparting photochromic properties, for example, by diffusion of aphotochromic coloring agent, as is well known in the art.

The polymerizable organic matrix of the invention is composed of (a)monomers selected from formulae I, II, III, and IV as defined above, (b)optionally, a photochromic coloring agent or dye, (c) optionally, achain transfer agent (CTA), (d) a radical polymerization initiator orcatalyst, and (e) optionally, a hindered amine light stabilizer (HALS).The various components of the inventive matrix is further describedbelow.

Monomers of formula I are well known and are commercially available. Oneparticularly preferred monomer of this class is Diacryl 121, which isavailable from Akzo Nobel, N.V., Nethedands, in which R═H and m and n=2.When this monomer is present in an amount below 50 wt. %, the matrixtends to exhibit excessive shrinkage during polymerization, leading topre-mold release, which in turn leads to material having poor opticalquality. Above 90 wt. %, the resulting material also tends to exhibitpoor optical quality.

Examples of monomers of formula II include, styrene and methylstyrene.Because styrene has a rather high refractive index (1.595), it has thebeneficial effect of increasing the refractive index of the organicmaterial. When styrene is present in an amount below 10 wt. %, thematerial tends to be of poor optical quality (i.e., birefringence due tomechanical stress), low strength, and low refractive index Above 30 wt.%, the matrix tends to stick to the mold during polymerization, and adecrease in the kinetics of the resulting photochromic material isobserved. By reduced kinetics in photochromic properties we mean thatthere is observed, slow darkening when the photochromic material isexposed a light source, and when the light source is eliminated, therate of lightening is also slow. In general, the faster the kinetics,the higher the thermal dependence. We have also observed that materialshaving excessively high thermal dependence have a tendency not to darkensufficiently when exposed to light. Therefore, there is a need to findan optimal amount of styrene and other monomers in order to have aproper balance of fast response and level of darkness achieved. Styreneis the preferred monomer of this class of monomers.

Monomers of formula III are represented by divinylbenzene anddi(methylvinyl)benzene. Divinyl benzene (DVB) is the preferred monomerof this class. We have found that when this monomer is absent, theresulting photochromic material tends to exhibit slow kinetics, and thelevel of darkening when the material is exposed to light is less thanoptimal. When this monomer is present in amounts in excess of 15 wt. %,excessive shrinkage is observed, leading to pre-mold release and opticaldefects. In addition, at amounts over 15 wt. %, the glass transitiontemperature (T_(g)) increases, but the mechanical strength decreases. Wehave found that kinetic properties, darkening level, molding, T_(g) andstrength are all optimized when this monomer is present in an amount inthe range of 2-4 wt. %. As is the case with styrene, the preferredmonomer, DN9B has a refractive index of 1.61, and therefore, it has theadditional beneficial effect of increasing the refractive index of thephotochromic material.

We have found that there is an optimal range of the ratio of the monomerof formula III to the monomer of formula II. In particular, we havefound that when the monomer of formula II is styrene, and the monomer offormula III is DVB, then preferably, the ratio of DVB:STYRENE is nogreater than 1.5, more preferably, it is in the range of 0.004-0.4, andmost preferably in the range of 0.08-0.24. For ease of discussion wewill refer to this ratio of DVB:STYRENE as R We have found that providedthe sum of DVB+STYRENE remains constant, the higher the value of K, thefaster the kinetics (darkening and lightening or fading), and the lowerthe impact strength. Also, the higher the value of R, the darker thephotochromic material when exposed to light. Finally, we have alsoobserved a slight increase in refractive index for a matrix which didnot contain the monomer of formula IV. As the value of R reduces, thereverse of the above observations is true.

The monomers of formula IV, the (meth)acrylic monomers, are alsowell-known products which are commercially available. Examples include,the butyl, pentyl, hexyl, heptyl, octyl, and 2-ethylhexyl(meth)acrylates (EHMA), as well as ethyltriglycol (meth)acrylate. Thepreferred monomer of this class is EHMA Below 1 wt. % the resultingmaterial exhibits low T_(g), making the material difficult to finish(grinding, polishing and edging). Therefore, it is desirable to havethis monomer is sufficient amount to overcome the above difficulty.However, because EHMA has a low refractive index (1.5), it also has thedisadvantage of lowering the refractive index of the photochromicmaterial Thus, at EHMA value at the lower limit of 1 wt. %, therefractive index of the resulting material is 1.575. However, at amountsin excess of 20 wt. %, the refractive index of the resultingphotochromic material drops to below 1.55. Generally, we have found thatthe optical quality of the photochromic composition, the T_(g), and thefinishing properties are optimized when this monomer is present in anamount in the range of 5-15 wt. %.

Thus, for the inventive organic material, by an appropriate choice andamounts of monomers it is possible to adjust the optical properties ofthe final material. For example, for photochromic materials, kineticproperties such as speed of darkening, speed of lightening, etc. may beadjusted as needed. In particular, by the addition of a monomer offormula II such as styrene to the dimethacrylic compound of formula I,it is possible to slow the kinetics of the coloring agents whichotherwise would be intrinsically too fast in the methacrylic matrix.Conversely, the incorporation of a third monomer selected from themonomers of formula III such as divinylbenzene, results in an increasein the speed or kinetics of a coloring agent which would otherwise betoo slow in the methyacrylic matrix. Thus, by a wise choice of theweight ratio of the monomer of formula II/monomer of formula III in adimethacrylic matrix as described above, it is possible to adjust thekinetic parameters of the photochromic process to a desired value,without altering the optical quality of the resulting materials, andwhile maintaining a high refractive index. The incorporation of thefourth monomer of formula IV in the proportions defined allows one toobtain more readily, thick lenses which are free of optical defects(distortions, stresses, cords, etc.) without altering properties such asthe glass transition temperature T_(g), the impact strength, or therefractive index.

The photochromic coloring agent can be chosen from the general classesof the spiroxazines, spiropyrans and chromenes which have photochromicproperties. Quite a few photochromic coloring agents of this type aredescribed in the literature and are available commercially. Usefulspiroxazines are described in co-pending, co-assigned French patentapplication by Chan, titled “Photochromic Spiroxazines, Compositions andArticles,” herein incorporated by reference. Spiroxazine coloring agentswhich can be used are described particularly in U.S. Pat. Nos.3,562,172, 4,634,767, 4,637,698, 4,720,547, 4,756,973, 4,785,097,4,792,224, 4,816,584, 4,831,142, 4,909,963, 4,931,219, 4,936,995,4,986,934, 5,114,621, 5,139,707, 5,233,038, 4,215,010, 4,342,668,4,699,473, 4,851,530, 4,913,544, 5,171,636, 5,180,524, 5,166,345 and inEP-A 0,508,219, 0,232,295, and 0,171,909, among others. Chromenes whichcan be used are described in U.S. Pat. Nos. 567,605, 4,889,413,4,931,221, 5,200,116, 5,066,818, 5,244,602, 5,238,981, 5,106,998,4,980,089, 5,130,058 and EP-A-0,562,915, among others. Furthermore,spiropyrans which can be used are generally described in“Photochromism,” G. Brown, Editor—Techniques of Chemistry—WileyInterscience—Vol. III—1971—Chapter III—Pages 45-294—R. C. Bertelson; and“Photochromism: Molecules & Systems,” Edited by H. Dürr—H.Bouas-Laurent—Elsevier 1990—Chapter 8: Spiropyrans—Pages 314-455—R.Guglielmetti. The teachings of all these patents and documents areincorporated here by reference.

On an indicative and nonlimiting basis, when one wishes to produce aphotochromic organic material, the proportion of photochromic coloringagent(s) to be incorporated in the polymerizable composition can rangefrom 0.01 to 10.0 wt %, preferably from 0.01 to 5 wt %, and morepreferably, from 0.05 to 1.0 wt. % with respect to the weight of themonomers.

Various combinations of coloring agents may be used in order to obtain adesired color or tint. For example, it is possible to use a combinationof photochromic coloring agents giving a gray or brown tint in thedarkened state. In one particularly useful embodiment, the photochromicdye consisted of a mixture of coloring agents comprising twospiroxazines and two chromenes. We have found the following specificcoloring agents to be particularly useful for the invention:

Dye Manufacturer Chemical type Blue D (Great Lakes) Spiroxazine Red PNO(Great Lakes) Spiroxazine Yellow L (Great Lakes) Chromene Sea Green(James Robinson Ltd.) Spiroxazine Berry Red (James Robinson Ltd.)Chromene

The chain transfer agent (CTA), can be incorporated in the polymerizablecomposition in a proportion of up to 5 wt. %, preferably, 0.01 to 2 wt.%, and more preferably in an amount in the range of 0.01 to 1.0 wt. %with respect to the monomers. For thin organic materials such as thinlenses measuring 2.0 mm in thickness or less, it may not be necessary toincorporate a CTA in the matrix However, for lenses greater than 2.0 mmin thickness, a CTA may be required in an amount within the statedranges. At amounts greater than 5 wt. % the T_(g) drops and the lensbecomes so soft as to make it difficult to finish the lens. We havefound that at an amount of about 0.9 wt. % a rather wide range of lensthicknesses (1.5-20 mm) can be manufactured. Preferably, the selectedCTA is a non-halogenated chain transfer agent because we have found thathalogenated CTAs tend to destroy the dye during polymerzation, and forsome dyes, halogenated CTAs may also lead to a gradual discoloration ofthe lens with use.

The chain transfer agent can be chosen from among, straight-chain C₂ toC₁₈, alkanethiols, alkanethiols substituted by at least one aryl oralkyl radical, and thiophenols. Straight-chain C₄ to C₁₆ alkanethiolsare preferred because they offer less volatility than the C₂ or C₃homologues. Specific examples are butanethiol, pentanethiol hexanethiol,heptanethiol, octanethiol, decanethiol, dodecanethiol, andtetradecanethiol. Another class of products which are useful as CTAs forthe invention include bis-merecaptoethyl ether (MEE), having the generalformula HS—CH₂CH₂—O—CH₂CH₂—SH. The preferred CTA for the invention isdodecanethiol.

We have found that for photochromic materials, the higher the amount ofCTA, the faster and the darker the resulting photochromic material.Also, as the level of CTA increases, the T_(g) decreases, strength(impact resistance stress) increases, refractive index decreases, andoptical quality (stress and striae) improves. As the level of CTAdecreases, the converse is true. For non-photochromic materials it isnot necessary to incorporate a CTA in the organic composition. If a CTAis to be used, non-halogenated CTAs are preferred as halogenated CTAsmay lead to discoloration.

For the photochromic material, any catalyst which will not react withthe coloring agent or dyes may be used. We have found that non-peroxideinitiators are particularly suited to the present photochronic material,preferably, initiators of the diazo type. These compounds are well-knownand available commercially. Examples of specific diazoic initiators areazobisisobutyronitrile (AIBN) and 2,2′-azobis(2-methylbutyronitrile)(AMBN), among others. The catalyst may be present in amounts in therange of 0.01 to 1.0 wt. %, preferably, 0.05 to 0.5 wt. % based on themonomers. At catalyst levels below about 0.05 wt. %, it becomesnecessary to increase the temperature significantly in order to initiatethe polymerization reaction Excessive temperature lead to “run-away”,making the process difficult to control. At catalyst levels above 0.5wt. %, excess amount of free radicals may be generated, and these freeradicals may destroy the dyes and lead to fatigue in the resultingphotochromic material. In addition, when the amount of initiator is over0.5 wt. %, the reaction may proceed so fast that it may be difficult tocontrol.

We have found that peroxide initiators such as the tert-butyl,isobutyryl, lauryl, benzoyl, and substituted benzoyl peroxides tend tointeract with the coloring agent and are therefore not useful for thepresent invention. Other examples of useful radical polymerizationinitiators can be found in “Polymer Handbook,” J. Brandrup and E. H.Immergut—Wiley Intersciences, Part II, pages 20 to 42. Therefore, when aphotochromic coloring agent is incorporated in the polymerizablecomposition for directly producing an organic material with photochromicproperties by copolymerization, it is appropriate to use a diazoicinitiator and to exclude the presence of any peroxide initiator in orderto prevent degradation of the photochromic coloring agent duringcopolymerization, as disclosed in the aforementioned French patentapplication.

The joint use of an alkanethiol as the chain transfer agent, and adiazoic compound as the initiator allows one to prepare a photochromicmaterial with excellent properties by radical polymerization in thepresence of at least one photochromic coloring agent. In particular, wehave found that the preferred chain transfer agents, the straight chainalkanethiols, have a chain transfer coefficient of zero with ourpreferred catalysts, the diazo compounds. Of course, fornon-photochromic materials, peroxide initiators may be used in additionto the diazo initiators.

We have found that the use of HALS in the present invention providesuseful stabilizing effect to the matrix. In the absence of HALS, theresulting photochromic material tends to discolor with use. That is, inthe clear state, the photochromic material exhibits an unintended tint.In one experiment, a blue discoloration was observed. In amounts greaterthan 2 wt. %, the HALS tends to hinder polymerization.

The invention also relates to articles consisting wholly or in part ofan organic materials according to the invention. Nonlimiting examples ofsuch articles are ophthalmic corrective lenses, sunglasses, glazings(e.g., windows) for vehicles or buildings etc. In these articles, theorganic material of the invention can constitute the whole thickness ofthe article (mass article) or can be in the form of a film or stratifiedlayer applied on a transparent organic or mineral support.

Ophthalmic lenses are the preferred articles and can be convenientlyproduced by polymerization in lens molds, for example, as described inU.S. Pat. No. 2,242,386, U.S. Pat. No. 3,136,000 or U.S. Pat. No.3,881,683.

For a better understanding of the invention, the following nonlimitingexamples are given. All the indicated proportions are parts by weight.In all the examples, the polymerization of the polymerizable compositionwas carried out in a lens mold under the following conditions: thepolymerizable composition is heated to 55° C. so as to bring about thethermal degradation of the diazoic compound with release of freeradicals; this temperature is maintained for 16 hours; the temperatureis then raised to 90° C., and this temperature is maintained for 2hours. Then, the lens obtained is removed from the mold and annealed at120° C. for 1 hours. The raw materials used in the examples are listedbelow:

Monomers:

Diacryl 121 of Akzo Chemical (DIA)

Styrene (STY)

Divinylbenzene (DVB)

2-ethylhexyl methacrylate (AEH)

Butyl methacrylate (MAB)

Ethyltriglycol methacrylate (MAET)

Catalysts (radical polymerization initiator):

2-2′ Azobis 2-methylbutyronitrile (AMBN)

Chain transfer agent (CTA):

1-dodecanethiol (DDT)

Photochromic coloring agent:

Red PNO, a spiroxazine marketed by the company Great Lakes.

EXAMPLES 1 TO 9

Eight compositions according to the invention were prepared, and theywere polymerized into plane lenses 2 mm thick (Examples 1-3, 7 and 8) orinto corrective lenses with −4 diopters with a thickness in the centerof 1.5 mm (Examples 4-6) by the general polymerization process describedabove. Table I which follows summarizes the formulations of thesepolymerizable compositions in wt. %.

TABLE I Coloring R = DVB Ex DIA STY DVB MAEH MAB MAET AMBN DDT Agent STY1 64 22 3 10 — — 0.2 1 0.02 0.136 2 64 22 3 — 10 — 0.2 1 0.02 0.136 3 6422 3 — — 10 0.2 1 0.02 0.136 4 58.4 24.8 5 — 10.8 — 0.2 1 — 0.202 5 64.322 2.2 — — 11 0.2 0.5 — 0.100 6 65.8 22.5 2.2 9 — — 0.2 0.5 — 0.098 762.6 21.4 4.3 — — 10.7 0.2 1 — 0.201 8 65.4 22.4 2.8 9 — — 0.2 0.4 —0.125 *9  62.4 19.4 4.0 13.0 0.2 0.9 .153 0.206 *This composition alsocontained 0.5 wt. % of a HALS.

All the lenses prepared from the compositions of Examples 1 to 9 abovewere of good optical quality: no visible stress in polarized light ordefects (cords, convection lines) were visible by shadowgraphic method.

In the lenses of Examples 1, 2, 3, and 9 the optical transmission at 560nm was measured before and after exposure for 15 min under a xenon lamp(40,000 lx), with the following results:

Transmission Before Transmission After Lens of Example Exposure (%)Exposure (%) 1 88.2 14.5 2 87.7 14.2 3 88.1 11.9 9 87.5 30.0

These lenses have good photochromic properties.

The lenses of Examples 4, 5, and 6 were subjected to the drop ball testdefined in “Use of Impact Resistant Lenses in Eyeglasses andSunglasses,” Code of Federal Regulation 21CFR 801-410 Washington D.C.,Apr. 1, 1990. All the lenses pass the test successfully.

Measurements of the refractive index n_(d20), of the Abbe number ν_(d),and of the glass transition temperature T_(g) were made on the lensesprepared in Examples 1 to 8, with the following results:

Lens of Example n_(d20) νd Tg, ° C. 1 1.5581 36.9 118 2 1.5581 36.7 1213 1.5599 36.7 113 4 1.5595 36.3 124 5 1.5588 37.0 112 6 1.5586 36.8 1217 1.5606 36.4 110 8 1.5594 36.5 — 9 1.5560 37.6 112

The Shore hardness D of the lens of Example 7 was also measured. It wasequal to 86.

As stated earlier, it is also contemplated by the present invention toprovide a method of forming a photochromic organic material having abase tint by first forming a photochromic material according the presentinvention, and subsequently imparting a tint to the photochromicmaterial by any known method such as by thermal diffusion (dipping orspraying). Any non-photochromic dye can be used provided such dyeexhibits little or no interaction with the photochromic dye. Thenon-photochromic dye can also be incorporated into the polymerizablematrix in the same manner as the photochromic dye provided thenon-photochromic dye is compatible with, and will not interact with, thephotochromic dyes.

The embodiments described above are illustrative and not exhaustive. Itwill be clear to persons skilled in the art that the above illustrationscan be modified, particularly by substitution of technical equivalents,without consequently leaving the intended scope of the invention.

What is claimed is:
 1. An organic photochromic material, said materialcomprising a copolymer of: (a) at least one monomer represented bygeneral formula (I),

in which R═H or CH₃ and m and n are, independently, 1 or 2; (b) at leastone aromatic monovinyl monomer represented by formula (II),

R₁═H or CH₃; and (c) at least one (meth)acrylic monomer represented byformula (IV), CH₂═C(R)—COOR′ in which R═H or CH₃ and R′ is a straight orbranched C₄ to C₁₆ alkyl radical, an alkylaryl radical, or apolyoxyethoxylated group with formula —(CH₂—CH₂O)_(n)R″ in which n=1 to10 and R″═CH₃ or C₂H₅; (d) at least one photochromic coloring agentselected from the group consisting of spiroxazines, spiropyrans,chromenes, and combinations thereof; and (e) optionally, one or morenon-photochromic coloring agents to impart a base tint to said materialand/or one or more hindered amine stabilizers.
 2. The organicphotochromic material according to claim 1 further comprising anaromatic divinyl monomer represented by formula (III),

where R₁═H or CH₃.
 3. The organic photochromic material according toclaim 1, further comprising at least one chain transfer agent.
 4. Theorganic photochromic material according to claim 3, wherein the chaintransfer agent is a non-halogenated chain transfer agent selected fromthe group consisting of straight chain alkanethiols, bis-mercaptoethylethers, and combinations thereof.
 5. The organic photochromic materialaccording to claim 3, wherein the chain transfer agent is a straightchain alkanethiol selected from the group consisting of butanethiol,pentanethiol, hexanethiol, heptanethiol, octanethiol, decanethiol,dodecanethiol, and tetradecanethiol.
 6. The organic photochromicmaterial according to claim 3, wherein the chain transfer agent is abis-mercaptoethyl ether having the general formulaHS—CH₂CH₂—O—CH₂CH₂—SH.
 7. The organic photochromic material according toclaim 1 comprising of 55 to 70 wt. % of at least one monomer representedby formula (I); 10 to 30 wt. % of at least one aromatic monovinylmonomer represented by formula (II); 1 to 20 wt. % of at least one(meth)acrylic monomer represented by formula (IV); and 0.01 to 10 wt. %of at least one photochromic coloring agent; said organic photochromicmaterial further comprising up to 15 wt. % of at least one aromaticdivinyl monomer represented by formula (III),

where R₁═H or CH₃; wherein the ratio of aromatic divinyl to aromaticmonovinyl monomers is in the range of 0 to 1.5.
 8. The organicphotochromic material according to claim 7, wherein the ratio ofaromatic divinyl to aromatic monovinyl monomers is in the range of 0.004to 0.4.
 9. The organic photochromic material according to claim 1,comprising of 55 to 70 wt. % of at least one monomer represented byformula (I); 15 to 25 wt. % of at least one aromatic monovinyl monomerrepresented by formula (II); 5 to 15 wt. % of at least one (meth)acrylicmonomer represented by formula (IV); and 0.01 to 5 wt. % of at least onephotochromic coloring agent; said organic photochromic material furthercomprising 2 to 6 wt. % of at least one aromatic divinyl monomerrepresented by formula (III),

where R₁═H or CH₃; wherein the ratio of aromatic divinyl to aromaticmonovinyl monomers is in the range of 0.08 to 0.24.
 10. An organicphotochromic material obtained by radical polymerization of apolymerizable composition comprising: (a) at least one monomerrepresented by general formula (I),

in which R═H or CH₃ and m and n are, independently, 1 or 2; (b) at leastone aromatic monovinyl monomer represented by formula (II),

R₁═H or CH₃; and (c) at least one (meth)acrylic monomer represented byformula (IV), CH₂═C(R)—COOR′ in which R═H or CH₃ and R′ is a straight orbranched C₄ to C₁₆ alkyl radical, an alkylaryl radical, or apolyoxyethoxylated group with formula —(CH₂—CH₂O)_(n)R″ in which n=1 to10 and R″═CH₃ or C₂H₅; (d) at least one photochromic coloring agentselected from the group consisting of spiroxazines, spiropyrans,chromenes, and combinations thereof; and (e) a non-peroxide radicalpolymerization initiator.
 11. The organic photochromic materialaccording to claim 10, wherein the polymerizable composition furthercomprises an aromatic divinyl monomer represented by formula (III),

where R₁═H or CH₃.
 12. The organic photochromic material according toclaim 10, wherein the polymerizable composition further comprises atleast one chain transfer agent.
 13. The organic photochromic materialaccording to claim 10, wherein the chain transfer agent is anon-halogenated chain transfer agent selected from the group consistingof straight chain alkanethiols, bis-mercaptoethyl ethers, andcombinations thereof.
 14. The organic photochromic material according toclaim 10, wherein the chain transfer agent is a straight chainalkanethiol selected from the group consisting of butanethiol,pentanethiol, hexanethiol, heptanethiol, octanethiol, decanethiol,dodecanethiol, and tetradecanethiol.
 15. The organic photochromicmaterial according to claim 10, wherein the chain transfer agent is abis-mercaptoethyl ether having the general formulaHS—CH₂CH₂—O—CH₂CH₂—SH.
 16. The organic photochromic material accordingto claim 10, wherein the polymerizable composition comprises: 55 to 70wt. % of at least one monomer represented by formula (I); 10 to 30 wt. %of at least one aromatic monovinyl monomer represented by formula (II);1 to 20 wt. % of at least one (meth)acrylic monomer represented byformula (IV); 0.05 to 0.5 wt. % of at least one non-peroxide radicalpolymerization initiator; 0.01 to 10 wt. % of at least one photochromiccoloring agent; and up to 5 wt. % of a chain transfer agent selectedfrom the group consisting of straight chain alkanethiols,bis-mercaptoethyl ethers, and combinations thereof; said organicphotochromic material further comprising up to 15 wt. % of at least onearomatic divinyl monomer represented by formula (III),

where R₁═H or CH₃.
 17. The organic photochromic material according toclaim 10, wherein the polymerizable composition further comprises one ormore non-photochromic coloring agents to impart a base tint to saidmaterial and/or one or more hindered amine stabilizers.
 18. A method ofmaking an organic photochromic material, said method comprisingradically polymerizing a polymerizable composition comprising: (a) atleast one monomer represented by general formula (I),

in which R═H or CH₃ and m and n are, independently, 1 or 2; (b) at leastone aromatic monovinyl monomer represented by formula (II),

R₁═H or CH₃; and (c) at least one (meth)acrylic monomer represented byformula (IV), CH₂═C(R)—COOR′ in which R═H or CH₃ and R′ is a straight orbranched C₄ to C₁₆ alkyl radical, an alkylaryl radical, or apolyoxyethoxylated group with formula —(CH₂—CH₂O)_(n)R″ in which n=1 to10 and R″═CH₃ or C₂H₅; (d) at least one photochromic coloring agentselected from the group consisting of spiroxazines, spiropyrans,chromenes, and combinations thereof; and (e) a non-peroxide radicalpolymerization initiator.
 19. The method according to claim 18, whereinthe polymerizable composition further comprises an aromatic divinylmonomer represented by formula (III),

where R₁═H or CH₃.
 20. The method according to claim 18, wherein thepolymerizable composition further comprises at least one chain transferagent.
 21. The method according to claim 20, wherein the chain transferagent is a non-halogenated chain transfer agent selected from the groupconsisting of straight chain alkanethiols, bis-mercaptoethyl ethers, andcombinations thereof.
 22. The method according to claim 20, wherein thechain transfer agent is a straight chain alkanethiol selected from thegroup consisting of butanethiol, pentanethiol, hexanethiol,heptanethiol, octanethiol, decanethiol, dodecanethiol, andtetradecanethiol.
 23. The method according to claim 20, wherein thechain transfer agent is a bis-mercaptoethyl ether having the generalformula HS—CH₂CH₂—O—CH₂CH₂—SH.
 24. The method according to claim 18,wherein the polymerizable composition comprises: 55 to 70 wt. % of atleast one monomer represented by formula (I); 10 to 30 wt. % of at leastone aromatic monovinyl monomer represented by formula (II); 1 to 20 wt.% of at least one (meth)acrylic monomer represented by formula (IV);0.05 to 0.5 wt. % of at least one non-peroxide radical polymerizationinitiator; 0.01 to 10 wt. % of at least one photochromic coloring agent;and up to 5 wt. % of a chain transfer agent selected from the groupconsisting of straight chain alkanethiols, bis-mercaptoethyl ethers, andcombinations thereof; said organic polymerizable composition furthercomprising up to 15 wt. % of at least one aromatic divinyl monomerrepresented by formula (III),

where R₁═H or CH₃.
 25. The method according to claim 18, wherein thepolymerizable composition further comprises one or more non-photochromiccoloring agents to impart a base tint to said material and/or one ormore hindered amine stabilizers.
 26. An article comprising an organicphotochromic material according to claim
 1. 27. The article according toclaim 26, wherein said article is an ophthalmic lens.
 28. The articleaccording to claim 26, wherein said article is a glazing for vehicles orbuildings.
 29. An article comprising an organic photochromic materialaccording to claim
 10. 30. The article according to claim 29, whereinsaid article is an ophthalmic lens.
 31. The article according to claim29, wherein said article is a glazing for vehicles or buildings.